Sand cores are commonly used within the foundry industry in the production of metal castings having complex interior and exterior geometry. These metal castings are formed by pouring molten metal around or into the sand core. After the casting process, the metal casting is extracted by destructively removing the sand core. Specifically, the metal casting is extracted by breaking the sand core or shaking the sand out of the casting. Hence, the casting of metal parts can require the use of one or more sand cores that correspond to the part geometry that is to be cast.
In general, the sand cores are formed in a core box. The core box typically includes two halves which cooperate to define a volume having the geometry of a desired sand core. Sand to be formed enters the core box through one or more blow tubes, which allow passage from a sand reservoir or magazine to the hollow interior of the core box. Before entering the magazine, the sand is coated with a liquid binder, often referred to as resin. The sand is conveyed from the magazine into the core box, via the blow tubes, by pressurizing the magazine with compressed air. Air is able to escape from the core box during the forming of the sand core through narrow vent passages in the core box.
In addition to filling the core box with sand, other steps are necessary before the desired sand core is completed. To refine the sand core shape before it is hardened, tamping may be used at the blow tube locations. Tamping involves flattening the residual sand at the blow tube locations to allow the sand core to best resemble the desired geometry. In past methods, tamping is accomplished by moving the magazine and blow tubes away from the core box, and subsequent positioning of a gassing head with tamping mechanisms over the core box. Tamping pins that correspond to the shape and location of the blow tubes are lowered into the blow tubes locations by a relative movement between the tamping mechanism, where the tamping pins are mounted, and the core box. Upon completion of the tamping, the catalyst gas is introduced to the sand core to cause a solidification thereof. The gas is introduced to the sand core via a gassing manifold encompassing the blow tube openings and the vents in the upper side of the core box. The gases exit the core box through vents in the lower side of the core box. After a suitable curing time, the core box is purged with air to remove any residual catalyst vapor. To complete the process, the core box halves are separated and the finished sand core is removed from the core box.
Recently, methods have been proposed that require complex blow tubes to facilitate the multiple functions of sand conveyance, tamping, sealing of the blow tube, and catalyst gas and purge air conveyance. U.S. Pat. No. 7,284,588 B2, hereby incorporated herein by reference in its entirety, discloses a complex blow tube that eliminates the need to interchange the sand magazine and gassing manifold during the machine cycle. This invention provides substantial advantages in terms of equipment cost and cycle time. However, the integration of separate conduits used for the conveyance of the sand and catalyst gas into the tamping pin and the necessity of maintaining adequate sealing is the source of disadvantages for this method. Examples of these disadvantages are the creation of a complex and tortuous flow path for the sand, a high risk of catalyst leakage causing blow tube plugging, laborious and costly cleaning of plugged blow tubes, and numerous rubber O-rings that are prone to fail with repeated use.
It would be desirable to have a sand core forming apparatus adapted to convey the sand, tamp the sand, and militate against an undesirable exposure of uncured sand residing within the blow tube to catalyst gases, while providing a non-tortuous flow path for the sand.